A known shaping device especially useful with an extruder or calibrator used for extrusion of thermoplastic material comprises at least one outlet-defining adjustably positionable unit lip, an opposing lip, at least one positioning member acting on the unit lip and a control and/or regulating mechanism for the thickness of the plastic product of the extruder.
The positioning member or effector is a part of the control and/or regulating mechanism and is a piezoelectric translator connected to a voltage source.
Of course the thickness of the extruded product downstream of the extruder tool or calibrator unit can be regulated or controlled, since the actual value of the thickness is measured and fed to the control and/or regulating mechanism in which the desired value is stored. Also the opposing lip can be controllable by at least one positioning member in the way described here.
It is known to control the piezoelectric translator in an analog fashion with different voltages. This is taught in German Patent Document No. 34 27 915. The size of the displacement produced depends on the size of the applied electric field and the so-called piezoelectric charge constant. This approach is successful but voltage amplification may be required. It is also possible to control the piezoelectric translator with a fixed voltage in the sense of an on/off control (digital control). That leads to a displacement between two fixed end points.